High permeability cube-on-edge oriented silicon steel and method of making it

ABSTRACT

Cube-on-edge oriented silicon steel and method of making it wherein the silicon steel is characterized by high permeability values. To the standard melt chemistry for cube-on-edge oriented silicon steel from about 0.002 to about 0.012 percent boron and from about 0.003 to about 0.010 percent nitrogen are added. The melt material is cast into ingots or slabs, reheated, hot rolled to hot band, annealed, pickled, cold reduced to final gauge, subjected to a decarburizing step and given a final high temperature anneal to produce the desired final orientation. The temperature of the anneal following hot rolling bears an inverse relationship to the final gauge of the silicon steel. Prior to the final anneal the silicon steel is provided with an annealing separator. A grain growth inhibitor may be provided in the environment of the stock during the primary grain growth stage of the final anneal so as to inhibit primary grain growth and to favor the growth of cube-on-edge oriented nuclei during the secondary grain growth stage.

United States Patent [191 Jackson 1 Mar. 25, 1975 [75] Inventor: John M.Jackson, Middletown, Ohio [73] Assignee: Armco Steel Corporation,

Middletown, Ohio 22 Filed: Mar. 1, 1973 21 Appl. No.: 337,073

[52] US. Cl 148/112, 148/3155, 148/111, 148/113 [51] Int. Cl. 1101f l/04[58] Field of Search 148/111-112, 148/113, 121, 122, 31.55; 75/123 B[56] References Cited UNITED STATES PATENTS 3,347,718 10/1967 Carpenteret al 148/111 3,575,739 4/1971 Fiedler 148/111 3,636,579 1/1972 Sakakuraet a1. 148/111 3,700,506 10/1972 Tanaka et a]. 148/111 3,725,143 4/1973Alworth et al. 75/123 B 3,764,406 10/1973 Littmann 148/111 PrimaryExaminer-Walter R. Sattcrfield Attorney, Agent, or Firm-Melville,Strasser, Foster & Hoffman [57 ABSTRACT Cube-on-edge oriented siliconsteel and method of making it wherein the silicon steel is characterizedby high permeability values. To the standard melt chemistry forcube-on-edge oriented silicon steel from about 0.002 to about 0.012percent boron and from about 0.003 to about 0.010 percent nitrogen areadded. The melt material is cast into ingots or slabs, reheated, hotrolled to hot band, annealed, pickled, cold reduced to final gauge,subjected to a decarburizing step and given a final high temperatureanneal to produce the desired final orientation. The temperature of theanneal following hot rolling bears an inverse relationship to the finalgauge of the silicon steel. Prior to the final anneal the silicon steelis provided with an annealing separator. A grain growth inhibitor may beprovided in the environment of the stock during the primary grain growthstage of the final anneal so as to inhibit primary grain growth and tofavor the growth of cube-on-edge oriented nuclei during the secondarygrain growth stage.

10 Claims, N0 Drawings 1 HIGH PERMEABILITY CUBE-ON-EDGE ORIENTED SILICONSTEEL AND METHOD OF MAKING liT BACKGROUND OF THE INVENTION nated (100)[001] in accordance with Millers indices.

As is well known, stocks having this orientation are characterized by arelatively high permeability in the rolling direction and a relativelylow permeability in a direction at right angles thereto. Cube-on-edgeoriented silicon steel has a number of applications, primary among whichis its use for the cores of magnetic apparatus such as transformers andthe like.

Silicon steels having the cube-on-edge grain orientation were firstproduced by Goss, as taught in U.S. Pat. No. 1,965,559. From the outset,however, silicon steels of this orientation with consistently goodmagnetic properties were difficult to produce on a commercial basis. Aaa consequence, prior art workers have devoted much time and effort tothe development of such silicon steels.

Over the years prior art workers have made rapid advances in thecommercial production of cube-on-edge oriented silicon steels. Forexample, in U.S. Pat. No. 2,287,467 Carpenter and Jackson taught aprocess of wet hydrogen decarburization enabling the removal of carbonand the harmful magnetic aging caused thereby. It had long beenrecognized that the formation of the cubeon-edge orientation involvedthe grain boundary energy phenomenon. It was further recognized that aninhibitor such as sulfur in the form of sulfides, if adequatelydispersed in the grain boundaries during the primary grain growth stageof the final anneal, would prevent the primary grain structure fromundergoing such grain growth as would interfere with subsequentsecondary grain growth. As a result, a fine grained matrix is maintaineduntil secondary grains of the cubeon-edge orientation begin to consumethe grains of other orientations. Thereafter, as the temperature risesfurther during the final anneal, secondary grain growth will proceed bygrain boundary energy and convert the fine grain matrix into a welldeveloped cube-on-edge structure. It was at first believed that theamount of inhibitor at the grain boundaries during the primary graingrowth stage of the final anneal depended upon the amount of inhibitorin the original melt and the amount of inhibitor lost during theprocessing steps ahead of the final anneal. As a consequence, many ofthese processing steps were considered critical in order to avoidinhibitor loss.

In U.S. Pat. No. 2,599,340 Littmann and Heck taught that superiorpermeabilities could be obtained in silicon-steels which were hot rolledto intermediate gauge from a high slab temperature of from 2,300F. Itwas determined that the high hot rolling temperature effected in part atleast the solution and subsequent precipitation of inhibitor such asmanganese sulfide in silicon iron. In U.S. Pat. No. 2,906,645 Carpenteret al taught the use of a magnesia annealing separator which, as a partof the process, produced an insulative mill glass on the finishedsilicon steel. Such a surface film or glass is highly desirable in manyapplications, providing electrical resistivity and protection againstoxidation or carburization.

In United States Letters Pat. No. 3,333,991; 3,333,992 and 3,333,993Kohler taught that an inhibitor could be provided in the environment ofthe silicon steel immediately prior to or during the primary graingrowth stage of the final anneal and could be caused to diffuse into thegrain boundaries. As a result, it was no longer necessary to rely solelyon the amount of inhibitor present in the initial melt, and many of theprocessing steps ahead of the final anneal came to be considered lesscritical. In accordance with the last mentioned patents, sulfur andcompounds thereof and selenium and compounds thereof may serve as theinhibitor. The inhibitor may be provided in the environment of thesilicon steel during the primary grain growth stage of the final annealin a number of ways. For example, sulfur or a sulfur compound whichdissociates or decomposes at the temperatures of primary grain growthmay be added to the annealing separator. On the other hand, theannealing atmosphere may be charged with hydrogen sulfide or any otherappropriate gaseous sulfur compound. In yet another variant procedure,hydrogen sulfide or any other appropriate gaseous sulfur compound may beadded to the atmosphere in the decarburizing step ahead of the finalanneal. The sulfur compound reacts with the iron surface to form acontrolled iron sulfide film on the material, providing a source ofsulfur during the primary grain growth stage of the final anneal.

The prior art workers finally reached a stage wherein a cube-on-edgeoriented silicon steel could consistently be produced on a commercialbasis having good magnetic characteristics, including a permeability atH=l0 oersteds averaging about 1820. Attention has since been centeredupon the improvement of these magnetic characteristics. In Unites StatesLetters Pat. No. 3,287,183 a method of making cube-on-edge orientedsilicon steel is taught wherein the product has a permeability at H=10oersteds of at least 1,800 and up to about l,9l0.'ln accordance withthis patent, the melt composition is critical and must include from0.025 to 0.085 percent carbon, from 2.5 to 4.0 percent silicon, from0.005 to 0.050 sulfur and, of special importance, from 0.010 to 0.065percent acidsoluble aluminum, the balance being iron and mixedimpurities. After hot rolling and pickling, the silicon steel is reducedto final gauge by one or more stages of cold rolling. Aside from themelt composition, it is critical that the last stage of cold rollingproduces a reduction of 81 to percent and that before the final coldrolling step the silicon iron be subjected to a high temperature annealsuch that aluminum nitrides are formed in the steel sheet in suchquantity that more than 0.0020 percent nitrogen stage of cold rolling bea high temperature anneal followed by a relatively rapid cool or quench.Finally, by virtue of the presence of aluminum oxide on the surface ofthe silicon steel, an ordinary insulative mill glass is difficult toform thereon.

United States Letters Pat. No. 3,700,506 teaches the use of a particularannealing separator in the process of the above mentioned U.S. Pat. No.3,287,183. In accordance with this teaching, a magnesium oxide separatoris used to which a titanium compound and a maganese compound have beenadded. To the annealing separator boron or a boron compound isadditionally added together with sulfur or a sulfur compound or seleniumor a selenium compound. The patent teaches that the boron or boroncompound when added with sulfur or selenium results in an improved coreloss in the final product and in the formation of a thin, uniform glassyfilm on the silicon steel. In this patent the boron or boron compound isused to control secondary grain growth during the final anneal, thealuminum nitrides being relied upon to control grain growth duringtheprimary grain growth stage of the final anneal.

The present invention is directed to the production of a cube-on-edgeoriented silicon steel having excellent magnetic characteristicsincluding a permeability at H=l oersteds of greater than about 1,820 andup to 1,900 or more. No unusually high temperature anneal is requiredprior to the final anneal; pickling may be readily accomplished in theusual manner; boron and nitrogen additions are made to control graingrowth during the primary grain growth stage of the final anneal; and aconventional insulative mill glass may be formed on the silicon steel asa part of its regular processing.

SUMMARY OF THE INVENTION The present invention contemplates the additionof boron and nitrogen in critical amounts to a conventional meltcomposition for cube-on'edge oriented silicon iron. The melt may alsocontain up to 0.008 aluminum.

Any suitable melt process may be employed. The melt can be either castas ingots or continuously cast slabs. Prior to hot rolling, the siliconsteel is heated to a temperature of from about 2,300 to about 2,550 andthereafter hot rolled to hot band. Following hot rolling, the siliconsteel is annealed within a temperature range of from about 1,500F toabout 2100F and the annealing temperature used bears an inverserelationship to the final gauge of the silicon steel. The anneal isfollowed by conventional pickling and cold rolling to final gauge in oneor more stages.

The cold rolled material is conventionally decarburized and coated witha magnesia (MgO) annealing separator. While not required, to achieveoptimum permeability values in the final product an inhibitor may beprovided in the environment of the silicon iron during the primary graingrowth stage of the final anneal. For example, from about 1 percent toabout 6 percent by weight of sulfur may be added to the magnesiaannealing separator The decarburized and coated material is thensubjected to a final anneal in a dry hydrogen atmosphere at atemperature of from about 2,000F to about 2,300F. Again, while not solimited, to achieve optimum permeability values the heat-up portion ofthe final anneal may be conducted in a nitrogen atmosphere, thetemperature being raised at the rate of less than about F per hour andpreferably about 50F per hour.

The cube-on-edge oriented silicon iron of the present invention ischaracterized by a permeability greater than about 1,820 and up to 1,900or beyond.

DESCRIPTION OF THE PREFERRED EMBODIMENNTS The melt contemplated by thepresent invention may be produced by any suitable and known method suchas by an openhearth furnace, a converter, an electric furnace, a vacuummelting furnace or the like.

The initial melt composition is conventional for the production ofcube-on-edge oriented silicon iron with respect to silicon, maganese,carbon and sulfur. However, to thismelt composition critical amounts ofboron and nitrogen are added. The melt composition may be stated inweight percent as follows: from about 2 percent to about 4 percentsilicon, from about 0.01% to about 0.15 percent (and preferably fromabout 0.03 percent to about 0.15 percent) manganese, from about 0.02percent to about 0.05 percent carbon, from about 0.01 percent to about0.03 percent sulfur, from about 0.002 percent to about .012% (andpreferably from about 0.003 percent to about 0.010 percent) boron, fromabout 0.003 percent to about 0.010 percent (and preferably from about0.004 percent to about 0.008percent) nitrogen, the balance being ironand those impurities incident to the mode of manufacture. While notrequired, aluminum may be present in the above stated melt composition(as a deoxidizer or impurity) in an amount up to about 0.008 percent.The optimum amount of boron is believed to be 0.007 percent and theoptimum amount of nitrogen is believed to be 0.007 percent.

The boron content of the initial melt can be achieved in any suitableand well known manner, including the addition to the initial melt of aboron-containing compound such as ferroboron. The nitrogen content ofthe initial melt can similarly be achieved by any suitable and wellknown means. For example, nitrogen may be added in the form of anitrogen compound such as nitrided manganese. Nitrogen may also be addedby blowing. Finally, the desired nitrogen content may be providedthrough the use of a melting process which normally results in anappropriate nitrogen content, as for example the use of the electricfurnace to produce a low carbon melt.

The silicon melt may be cast either as ingots or continuously castslabs. 1f the steel is cast into ingots, the ingots can be eitherdirectly hot rolled to hot band, or alternatively, they can be rolled toslabs of intermediate thickness, which slabs are subsequently reheatedand hot rolled to hot band. When hot rolling slabs formed from ingots orslabs from a continuous caster, the slabs should be reheated prior tohot rolling to a temperature in the range of from about 2,400F to 2,550F(and preferably about 2,500F) in accordance with the above mentionedU.S. Pat. No. 2,599,340. The final hot band will normally have athickness of from about 0.050 to about 0.10 inch.

After hot rolling to hot band, the silicon steel is annealed at atemperature of from about 1,500F to about 2,100F, and preferably fromabout 1,700F to about 2,000F for about 3 /2 minutes in any appropriateatmosphere such as air, products of combustion, etc. It has beendetermined that to obtain optimum permeability values the temperature ofthis anneal bears an inverse relationship to the desired final thicknessof the silicon steel. Thus, when thinner final sheet stock is to beproduced, the temperature of this anneal should fall within the upperportions of the above stated ranges. Similarly, when thicker sheet stockis to be produced, the temperature of this anneal should fall within thelower portion of the above stated ranges. The annealed, hot rolledsilicon steel may be spray quenched or air cooled. The silicon steel isthereafter conventionally pickled and cold reduced in a single stage (orin two or more stages with intermediate anneals) to final gauge.

The cold reduced silicon steel is decarburized in a wet hydrogenatmosphere at a temperature of about 1,500F and a dewpoint of about 135,in accordance with the above mentioned U.S. Pat. No. 2,287,467.

After the decarburization step, the silicon steel is provided with anappropriate annealing separator such as magnesia, alumina, calcium oxideor mixture of these. When it is desired to have a mill glass formed uponthe finished product, a magnesia annealing separator can be used inaccordance with the above noted U.S. Pat. No. 2,906,645. The magnesiaseparator may be applied to the silicon steel in any of the conventionaland well known ways.

The silicon steel, having been provided with an annealing separator, issubjected to a final box anneal at a temperature of from about 2,000F toabout 2,300F, and preferably about 2,200F for a period of time of fromabout 8 to about hours. This anneal, designated herein as the finalanneal for purposes of clarity, is that anneal during the secondarygrain growth stage of which the cube-on-edge orientation is achieved.The anneal is conducted in a dry hydrogen atmosphere.

While to obtain good permeability values it is not necessary, it hasbeen determined that to obtain optimum permeability values an inhibitorshould be provided in the environment of the silicon steel immediatelyprior to or during the primary grain growth stage ofthe final anneal.Sulfur, selenium, and their compounds will serve as excellent inhibitormaterial and the provision of this material in the environment of thesilicon steel may be accomplished in any of those ways described by theabove noted U.S. Pat. Nos. 3,333,991; 3,333,992 and 3,333,993. Forexample, excellent results have been achieved when the magnesiaannealing separator contains from about 1 percent to about 6 percent byweight of sulfur.

While again it is not required for purposes of this invention, it hasnevertheless been found that to obtain optimum magnetic properties anitrogen atmosphere should be used during the heat-up portion of the anneal, dry hydrogen being substituted therefore during the remainder ofthe annealing treatment. The heat-up portion of the anneal should have arelatively slow temperature rise of less than about 125F per hour andpreferably about 50 per hour.

Examples of the present invention may be given as follows:

EXAMPLE 1 A lab melt under vacuum was prepared having the followinganalysis in weight percent:

An ingot was cast and heated to l,900F. The material was thereafter hotrolled to 0.100" and annealed at l,900F for 3 /2 minutes. Following thisanneal, the silicon steel was air cooled, pickled and cold reduced in asingle stage to 0.012 in.

The cold reduced silicon iron was decarburized at l,500F in wet hydrogenat a dewpoint of F. Thereafter, the silicon steel was coated with amagnesia annealing separator containing 6 percent by weight of sulfur.Finally, the coated silicon steel was box annealed in a hydrogenatmosphere at 2,200F for 30 hours. The finished material was determinedto have a straight grain permeability at H=l0 oersteds of 1921.

The above example illustrates the high permeability achievable when bothboron and nitrogen are added to the melt within the ranges given aboveand the silicon steel is processed in accordance with the presentinvention.

EXAMPLE 2 A laboratory heat was produced having the following analysisin weight percent:

The material was cast into 1 inch thick ingots. The ingots were heatedto l,900F and hot rolled to approximately 0.09 in. First and secondsamples of this material were annealed at 1,700F for 3 /2 minutes. Athird sample was annealed at 2,100F for 3 /2 minutes. The first samplewas air cooled and cold rolled to 14 mils. The second and third sampleswere each spray quenched and cold rolled to 10 mils.

All three samples were decarburized at 1500F in wet hydrogen at adewpoint of 135. All samples were coated h a magnesia n alin e tatqrsntaiains EXAMPLE 3 A laboratory heat was prepared with the followinganalysis in weight percent:

wZO a The material was cast into 1 inch thick ingots, heated to 1,900Fand hot rolled to approximately 0.09 inches. The material was annealedat 1,700F for 3% minutes, air cooled, pickled and cold rolled to athickness of 14 mils. The cold rolled silicon steel was decarburized at1,500F in wet hydrogen at a dewpoint of 135 and was coated with amagnesia separator containing 6 percent by weight of sulfur. The coatedsilicon steel was given a final anneal at 2,200F for 27 hours with aheat-up rate of 50 per hour. During the heat-up portion of the finalanneal a nitrogen atmosphere was used, a hydrogen atmosphere being usedthroughout the remainder of the anneal. The final product demonstrated apermeability at H= oersteds of 1,889.

Modifications may be made in the invention without departing from thespirit of it.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A method of making cube-on-edge oriented silicon steel comprising thesteps of preparing a silicon steel melt having a composition in weightpercent consisting essentially of from about 2 to about 4 percentsilicon, from about .01 to about 0.15 percent manganese, from about 0.02to about 0.05 percent carbon, from about 0.01 to about 0.03 percentsulfur, from about 0.003 to about 0.010 percent boron, from about 0.003to about 0.010 percent nitrogen, up to 0.008 percent aluminum, thebalance being iron and impurities incident to the mode of manufacture,casting said silicon steel melt, reheating said silicon steel at atemperature of from about 2,300F to about 2,550F, hot rolling saidsilicon steel to an intermediate thickness of from about 0.050 to about0.100 in., annealing said hot rolled silicon steel at a temperature offrom about 1,500F to about 2,100F, pickling said annealed silicon steeland cold reducing it to final gauge, decarburizing said cold reducedsilicon steel, providing an annealing separator for said decarburizedsilicon steel and subjecting said silicon steel to a final box anneal indry hydrogen at a temperature of from about 2000F to about 2,300F forfrom about 8 to about 30 hours, whereby to provide a cube-on-edgeoriented silicon steel having a permeability at H=10 oersteds greaterthan 1820.

2. The process claimed in claim 1 wherein said melt composition inpercent by weight consists essentially of from about 2 to about 4percent silicon, from about 0.03 to about 0.15 percent manganese, fromabout 0.02 to about 0.05 percent carbon, from about 0.01 to about 0.03percent sulfur, from about 0.003 to about 0.010 percent boron, fromabout 0.004 to about 0.008 percent nitrogen, the balance being iron andimpurities incident to the mode of manufacture.

3. The process claimed in claim 1 wherein said final anneal has aprimary grain growth stage and a secondary grain growth stage, providinga grain growth inhibitor in the environment of said silicon steel duringsaid primary grain growth stage, said grain growth inhibitor beingchosen from the class consisting of sulfur, sulfur compounds, seleniumand selenium compounds.

4. The process claimed in claim 1 wherein said annealing separatorcomprises magnesia containing from about 1 percent to about 6 percentsulfur by weight.

5. The process claimed in claim 1 wherein said final box anneal has aheat-up period, said heat-up period being conducted in a nitrogenatmosphere, the remainder of said box annealing being conducted in saiddry hydrogen atmosphere.

6. The process claimed in claim 1 wherein said anneal following said hotrolling is conducted at a temperature of from about 1,700F to about2,000F, said temperature range bearing an inverse relationship to saidfinal gauge of said silicon steel.

7. The process claimed in claim 2 wherein said melt contains about 0.007boron and about 0.007 percent nitrogen.

8. The process claimed in claim 2 wherein said anneal following said hotrolling is conducted at a temperature of from about l,700F to about2,000F, said last mentioned temperature range bearing an inverserelationship to said final gauge of said silicon steel, said annealingseparator comprising magnesia containing from about 1 percent to about 6percent sulfur by weight, said final anneal having a heat-up stage, saidheat-up stage being conducted with a nitrogen atmosphere, the remainderof said final box anneal being conducted in said dry hydrogenatmosphere, the temperature of said heat-up stage being raised at therate of less than about F per hour.

9. The process claimed in claim 5 wherein said final box anneal has aheat-up stage, said temperature of said final anneal being raised duringsaid heat-up stage at the rate of less than 125 per hour.

10. A cube-on-edge oriented silicon steel having a permeability at H=l0oersteds greater than 1,820 and made in accordance with the process ofclaim 1.

1. A METHOD OF MAKING CUBE-ON-EDGE ORIENTED SILICON STEEL COMPRISING THESTEPS OF PREPARING A SILICON STEEL MELT HAVING A COMPOSITION IN WEIGHTPERCENT CONSISTING ESSENTIALLY OF FROM ABOUT 2 TO ABOUT 4 PERCENTSILICON, FROM ABOUT 01 TO ABOUT 0.15 PERCENT MANGANESE, FROM ABOUT 0.02TO ABOUT 0.05 PERCENT CARBON, FROM ABOUT 0.01 TO ABOUT 0.03 PERCENTSULFUR, FROM ABOUT 0.003 TO ABOUT 0.010 PERCENT BORON, FROM ABOUT 0.003TO ABOUT 0.010 PERCENT NITROGEN, UP TO 0.008 PERCENT ALUMINUM, THEBALANCE BEING IRON AND IMPURITES INCIDENT TO THE MODE OF MANUFACTURE,CASTING SAID SILICON STEEL MELT, REHEATING SAID SILICON STEEL AT ATEMPERATURE OF FROM ABOUT 2,300*F TO ABOUT 2,550*F, HOT ROLLING SAIDSILICON STEEL TO AN INTERMEDIATE THICKNESS OF FROM ABOUT 0.050 TO ABOUT0.100 IN., ANNEALING SAID HOT ROLLED SILICON STEEL AT A TEMPERATURE OFFROM ABOUT 1,500*F TO ABOUT 2,100*F, PICKLING SAID ANNEALED SILICONSTEEL AND COLD REDUCING IT TO FINAL GAUGE, GAUGE, DECARBURIZING S COLDREDUCED SILICON STEEL, PROVIDING AN ANNEALING SEPARATOR FOR SAIDDECARBURIZED SILICON STEEL AND SUBJECTING SAID SILICON STEEL TO A FINALBOX ANNEAL IN DRY HYDROGEN AT ATEMPERATURE OF FROM ABOUT 2000*F TO ABOUT2,300*F FOR FROM ABOUT 8 TO ABOUT 30 HOURS, WHEREBY TO PROVIDE ACUBE-ON-EDGE ORIENTED SILICON STEEL HAVING A PERMEABILITY AT H=10OERSTEDS GREATER THAN
 1820. 2. The process claimed in claim 1 whereinsaid melt composition in percent by weight consists essentially of fromabout 2 to about 4 percent silicon, from about 0.03 to about 0.15percent manganese, from about 0.02 to about 0.05 percent carbon, fromabout 0.01 to about 0.03 percent sulfur, from about 0.003 to about 0.010percent boron, from about 0.004 to about 0.008 percent nitrogen, thebalance being iron and impurities incident to the mode of manufacture.3. The process claimed in claim 1 wherein said final anneal has aprimary grain growth stage and a secondary grain growth stage, providinga grain growth inhibitor in the environment of said silicon steel duringsaid primary grain growth stage, said grain growth inhibitor beingchosen from the class consisting of sulfur, sulfur compounds, seleniumand selenium compounds.
 4. The process claimed in claim 1 wherein saidannealing separator comprises magnesia containing from about 1 percentto about 6 percent sulfur by weight.
 5. The process claimed in claim 1wherein said final box anneal has a heat-up period, said heat-up periodbeing conducted in a nitrogen atmosphere, the remainder of said boxannealing being conducted in said dry hydrogen atmosphere.
 6. Theprocess claimed in claim 1 wherein said anneal following said hotrolling is conducted at a temperature of from about 1, 700*F to about2,000*F, said temperature range bearing an inverse relationship to saidfinal gauge of said silicon steel.
 7. The process claimed in claim 2wherein said melt contains about 0.007 boron and about 0.007 percentnitrogen.
 8. The process claimed in claim 2 wherein said annealfollowing said hot rolling is conducted at a temperature of from about1, 700*F to about 2,000*F, said last mentioned temperature range bearingan inverse relationship to said final gauge of said silicon steel, saidannealing separator comprising magnesia containing from about 1 percentto about 6 percent sulfur by weight, said final anneal having a heat-upstage, said heat-up stage being conducted with a nitrogen atmosphere,the remainder of said final box anneal being conducted in said dryhydrogen atmosphere, the temperature of said heat-up stage being raisedat the rate of less than about 125*F per hour.
 9. The process claimed inclaim 5 wherein said final box anneal has a heat-up stage, saidtemperature of said final anneal being raised during said heat-up stageat the rate of less than 125* per hour.
 10. A cube-on-edge orientedsilicon steel having a permeability at H 10 oersteds greater than 1,820and made in accordance with the process of claim 1.